Urinary System Flashcards
How do the kidneys regulate different aspects of homeostasis?
- Balance water with antidiuretic hormone (ADH)
- Maintain blood plasma so molarity by controlling plasma ionic comp through aldosterone
- maintain blood pressure and volume by releasing renin (low blood pressure)
- regulate plasma pH to maintain acid-base balance
- secrete erythropoietin to stimulate RBC production when low O2 levels are detected
- activate vitamin D3 for calcium homeostasis
What are the functions of the urinary system?
- Regulate many aspects of homeostasis through the kidneys and hormones (renin, ADH, calcitriol)
- Eliminate metabolic waste products like nitrogenous wastes from protein synthesis, excess ions, toxins, and drugs
What are the primary structures of the urinary system and their functions?
- Kidneys- form urine
- Ureters- transport urine from kidneys to the bladder
- Bladder- Stores urine
- Urethra- excretes urine from bladder to outside of body
What are the major developmental aspects of the urinary system?
- functional kidneys developed by the 12th week in utero
- Fetus produces urine that adds to amniotic fluid ~week 13
- newborn urinary system under developed (small bladder, not concentrated for 2-3 months postpartum, voids up to 40x/day)
How is blood supply impacted by the kidneys?
- a quarter of the body’s total blood supply passes through the kidneys each minute
- renal artery provides each kidney with arterial blood supply
What is the path of blood through the kidneys? (Know pathway starting from either end)
Aorta-> renal artery-> segmental artery-> interlobar artery-> arcuate artery-> cortical radiate artery-> afferent arteriole-> glomerulus (capillaries)-> efferent arteriole-> peritubular capillaries -> cortical radiate vein-> arcuate vein-> interlobar vein-> renal vein-> inferior vena cava
What are the major features of the kidney?
- right kidney is slightly lower than the left due to the positioning of the liver
- renal hilum is a medial indentation where structures (ureters, renal blood vessels, and nerves) enter or exit the kidneys
- adrenal gland sits atop each kidney
Explain the basics of what occurs during a kidney transplant
- Two surgeries take place
- First is removing diseased kidney, second is giving transplant
- Kidney only lasts ~12 years
What are some of the major causes of kidney disease?
- Lack of blood flow to kidneys
- severe dehydration
- Type I and Type 2 Diabetes Melkite’s
- Infections
- Genetics
- Street Drug Use
- Long term use of non-steroidal anti-inflammatory drugs (NSAIDs like ibuprofen and naproxen)
What are some of the major symptoms of kidney disease?
- Hypertension
- nausea
- vomiting
-loss of appetite - decreased mental acuity
- proteinuria
- weakness
What are kidney stones?
- Hard mass that forms from crystals in the urine usually stopped by natural chemicals in the urine
- most often made of calcium oxalate (Can sometimes be calcium phosphate, Struve the, Uris acid, cystine stones, and more)
- causes can be dietary, genetic, excessive dehydration, high protein diet, gout
- having one kidney stone makes it more likely to happen again
What is a nephron?
- Structural and functional units of the kidney
- responsible for forming urine
Describe the structure of a nephron
- renal tubules that extend from the glomerular capsule and end at the collecting duct
- made of: glomerular (Bowman’s) capsule, proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT)
What is the renal corpuscle?
- Composed of Bowman’s Capsule (site of filtration) and the glomerulus (tuft of capillaries)
- Site of filtration (blood is filtered from glomerular capillaries into Bowman’s capsule to start forming urine)
What are the different types of nephrons?
- Cortical nephrons (located mostly in the cortex of the kidney and makes up most nephrons)
- Juxtamedullary nephrons (found at boundary of the cortex and dip deep into the medulla- located next to the corpuscle)
What are the different capillaries associated with the nephron?
- glomerulus
- peritubular capillary bed (wrap all around and are involved in gas exchange)
- Vasa recta (only present in juxta medullary nephrons; specialized capillaries that run along the loop of Henle)
What is the glomerulus?
- Knot of capillaries
- Capillaries are covered with podocytes from the renal tubule
- sits within a glomerular capsule
- Under high pressure to force fluid and small solutes out of blood and into the glomerular capsule
- Fed and drained by arteriole (afferent feeds; efferent drains)
- Specialized for filtration
What is GFR and how is it impacted by BP?
- Glomerular filtration rate
- Increased by increase in BP due to increased capillary hydrostatic pressure
- Relatively constant with increases in BP due to intrinsic regulation until BP reaches 180 mmHg
- Decreases with decreases in BP (<80mmHg); decreases water filtered + urine excretion
What is the afferent arteriole?
- Arises from a cortical radiate artery
- Feeds the glomerulus
What is the efferent arteriole?
- Receives blood that has passed through the glomerulus (Drains glomerulus)
What are the peritubular capillary beds?
- Arise from efferent arteriole
- Regular, low pressure capillaries
- Adapted for reabsorption instead of filtration
- Cling close to the renal tubule to reabsorb some substances from tubules
What are the collecting ducts?
- Receives urine from many nephrons
- Run through the medullary pyramids
- Delivers urine into the calyces and renal pelvis
What type of process is urine formation?
- an active recall process
- Occurs at the glomerulus
What are the steps of urine formation?
1) Glomerular Filtration (always first)-> Water and solutes smaller than proteins are forced through the capillary walls and pores of the glomerular capsule into the renal tubule
2) Tubular Reabsorption -> Water, glucose, amino acids, and needed ions are transported out of the filtrate into the tubule cells and then enter the capillary blood
3) Tubular Secretion-> H+, K+, creatinine, and drugs are removed from the peritubular blood and secreted by the tubule cells into the filtrate
*Steps 2 and 3 are interchangeable
What are the sites of filtration, reabsorption, and secretion in a kidney?
- Filtration occurs in the glomerular capsule
- Reabsorption occurs in the proximal tubule, distal tubule, the Loop of Henle, and collecting duct
- Secretion occurs in the proximal tubule and distal tubule
*See slide 23 for diagram
Describe the basic renal processes
- Glomerular filtration occurs from the glomerulus to Bowman’s capsule
- Reabsorption is from tubules to peritubular capillaries
- Secretion is from peritubular capillaries to tubules
- Excretion is from tubules out of body
*See slide 24 for diagram
What is the process that occurs in glomerular filtration?
- It is a mostly none selective passive process dictated by the size of the solute
- Water and solutes smaller than proteins are forced through capillary walls
- Proteins and blood cells are normally too large to pass through the filtration membrane
- Filtrate is collected in the glomerular capsule and leaves via the renal tubule
What is the average GFR/day?
125 mL/min or 180 L/day
What happens to GFR during kidney failure?
The kidney can only filter 2x a week so toxins build up and have to be filtered all at one
- extremely exhausting process helped externally by dialysis (expensive)
What is the process of reabsorption?
- Movement from tubules into peritubular capillaries (returned to blood)
- Mostly occurs in proximal tubule
- most is not regulated
- barrier reabsorption is epithelial cells of renal tubules and endothelial cells of capillary (minimal)
What is the process of tubular reabsorption?
- peritubular capillaries reabsorb useful substances (water, glucose, amino acids, ions)
- Mostly active process
- Most often occurs in the proximal convoluted tubule
- Some materials are not reabsorbed (nitrogenous waste products, Uris acid from nuclei acid breakdown, creatinine associated with creating metabolism in muscles)
How does reabsorption occur in the proximal tubule?
- Proximal tubule is a mass reabsorber
- non-regulated reabsorption
- brush border has a large surface area due to microvilli
- approximately 70% water and sodium reabsorbed
-100% glucose reabsorbed (with a normal diet)
What is the process of tubular secretion?
- Reabsorption in reverse
- the movement of materials from peritubular capillaries into the renal tubules
- important for getting rid of substances not already in the filtrate
- materials left in the renal tubule move toward the ureter
- Secreted substances (potassium, hydrogen ions, choline, creatinine, penicillin)
What is excretion rate?
- amount of substance excreted = amount filtered + amount secreted - amount reabsorbed
- amount excreted depends on rate of filtration, secretion rate, and reabsorption rate
Describe the renal handling of solute
- if amount of solute excreted per minute is less than filtered load, solute was reabsorbed
- if amount of solute excreted per minute is greater than filtered load, solute was secreted (ex. Meds are secreted)
What is clearance (mL/min)?
- Volume of plasma from which a substance has been removed by kidneys per unit time
- clearance of inulin (not same as insulin; is a carbohydrate) can be used to measure GFR (measures glomerular function)
- Calculation: excretion rate/conc. In plasma
- can be performed if a doctor suspects a pathology
What is renal plasma flow rate and how is it measured?
- it’s the clearance of a substance freely filtered, fully secreted, and not reabsorbed
- Measured with para-aminohippuric acid (PAH)
- Measures blood flow through kidney to find out if it’s hindered at some point
- avg. = 550-650 mL/min
- amount excreted = amount contained in volume of plasma that entered the kidneys
Describe the structure of the urinary bladder
- smooth, collapsible, muscular sac
- temporarily stores urine
- moderately full bladder ~12.5cm + holds ~500mL of urine
- Trigone is a triangular region of the bladder base
- has three openings (2 from ureters coming in + 1 from urethra leaving)
- prostate gland surrounds neck of bladder in males
What is the structure of the urinary bladder wall?
- 3 layers of smooth muscle collectively called the detrusor muscle
- mucosa made of transitional epithelium that allows that bladder to not increase internal pressure
- walls are thiick and folded in an empty bladder
- can expand significantly without increasing internal pressure due to transitional epithelium
- External urethral sphincter under voluntary control
- internal urethral sphincter under involuntary control
What is the process of micturition (voiding/urination)?
- urine formed in renal tubules
- fluid drains into renal pelvis and into ureter
- ureters lead to bladder + store urine until excretion
- both sphincter muscles open to allow voiding
- internal urethral sphincter is relaxed after stretching of the bladder
- pelvic splanchinic nerves initiate bladder to go into reflex contractions
- urine is forced past the internal urethral sphincter and personal feels urge to void
external urethral sphincter must be voluntarily relxed to void
What are the major characteristics of urine?
- 1-1.8 L of urine produced in 24 hours (depending on fluid intake)
- urine + filtrate are different
- filtrate contains everything blood plasma does except proteins
- urine is what remains after filtrate has lost most of its water, nutrients, and necessary ions
- urine contains notrogenous wastes + substances that aren’t needed
- yellow color due to pigment urochrome (from destruction of hemoglobin) + solutes
- slightly aromatic
- varying pH but usually acidic (~6)
- specific gravity of 1.001-1.035
What is specific gravity
It is the density of urine relative to water
Why are multivitamins not recommended?
- Not regulated by FDA
- things like Vitamin C tablets are water soluble + are just peed out (filtered by kidney)
What solutes are usually found in urine?
- sodium + potassium ions
-urea, uric acid, creatinine - ammonia
- bicarbonate ions
- things we have excess of
What solutes are not normally found in urine?
- glucose
- large proteins
- RBCs
- hemoglobin
- white blood cells
- bile
What is glycosuria?
- glucose in urine
- Nonpathalogical causes: Excessive intake of sugary foods
- Pathalogical causes: Diabetes mellitus
What is proteinuria
- proteins in urine
- Nonpathological causes: Physical exertion, pregnancy (preeclampsia)
- pathalogical causes: Glomerulonephritis, hypertension
What is pyuria?
- WBCs in urine
- Causes: UTI
What is hematuria?
- RBCs in urine
- Causes: Bleeding in urinary tract due to trama, kidney stones, infection
What is hemoglobinuria?
- Hemoglobin in urine
-Causes: Transfusion reaction, hemolytic anemia
What is bilirubinuria?
- bile pigment in urine
- Causes: liver disease (hepatitis) from viral infection
How do the kidneys impact blood composition?
- BC depends on diet, cellular metabolism, and urine output
- Kidneys maintain BC through excretion of wastes, maintaining water balance of the blood, maintaining electrolye balance of the blood, ensuring proper blood pH
What is osmolarity’s role in reabsorption
- No osmotic force for water to move between fluid compartments
- kidneys compensate for changes in osmolarity of extracellular fluid by regulating water reabsorptiion
- Water reabsorption occurs in the proximal tubule (passive based on osmotic gradient, follows solute reabsorption, primary solute that follows water is sodium
- osmolarity of body fluids = ~300 mOsm/L
What is obligatory water loss and why is it necessary?
- Minimum volume of water that must be excreted in the urine per day
- 440mL a day (minimum)
- lost through breathing, skin, urine, more
- necessary to eliminate non-reabsorbed solutes
- max osmolarity urine= 1200-1400 mOsm/L (concentrated)
- min urine osmolarity= 100mOsm/L (dilute)
-some solute must be excreted
How is water balance maintained?
- dilute urine in larger volumes is produced if water intake exceeds need (can lead to hyponatremia)
- less urine that is concentrated is produced when a person is dehydrated (hypernatremia)
- proper concentrations of various electrolytes must also be present
What is hyponatremia?
- Overhydrating
- When blood volumbe doesn’t have enough sodium
- Water intoxication
What is hypernatremia?
- too much sodium in blood volume due to dehydration
Why is the counter-current multiplier in the Loop of Henle important?
- establishes an osmotic gradient that is dependent on the Loop of Henle
- requires a lot of ATP to maintain it
What role does the descending limb of the Loop of Henle have in the osmotic gradient?
- it’s permeable to water/aquaporins
- no transport of Na+, Cl-, or K+
What role does the ascending limb of the Loop of Henle have in the osmotic gradient?
- impermeable to water
- transport of Na+, Cl1, and K+/pumps
What is the result of the counter-current multiplier?
- Fluid in proximal tubule at 300 mOsm/L
- Osmolarity of fluid in descending limb increases as it descends (becomes more concentrated)
- Osmolarity of fluid in ascending limb decreases as it ascends (dumping off ions + vasa recta will pick some up)- becomes more dilute
What is the purpose of the vasa recta?
-prevents dissipation of the osmotic gradient while supplying nutrients + removing waste by picking up extra water
- blood in vasa recta removes wter leaving the loop of Henle (prevents water from diluting conc gradient)
How is water and electrocute reabsorption regulated?
- Osmoreceptors create loop
What are osmoreceptors?
- cells in the hypothalamus
- react to changes in blood composition by becoming more active as osmolarity increases, fire more APs
- leads to release of antidiuretic hormone (ADH)
- ADH decreases osmolarity (part of negative feedback response
What is the negative feedback loop that regulates water and electrolyte reabsorption?
Water reabsorption-> plasma osmolarity/ circulatory BV-> signals baroreceptors and osmoreceptors-> osmoreceptors signal ADH synthesis + baroreceptors signal ADH release-> signals kidney collecting duct receptors-> cAMP-> aquaporin-2 -> water reabsorption
When is ADH released?
- when osmolarity is high
- dependent on osmotic-gradient established by counter-current multiplier
What is water permeability dependent on?
- Water channels
- aquaporin-3 (present in basolateral membrane)
- aquaporin-2 (present in apical membrane when ADH is present in blood)
- both must be present for water to be reabsorbed into peritubular capillary
What happens to the permeable membrane in the presence of ADH?
ADH stimulates insertion of water channels (aquaporin-2) into apical membrane
- water can permeate membrane and be reabsorbed by osmosis
- Max osmolarity urine (1200-1400 mOsm/L
How is ADH release regulated?
- released from neurosecretory cells originating in the hypothalamus
- primary stimulus for release is increased osmolarity (osmoreceptors) of plasma
- Decreased blood pressure (baroreceptors) and decreased BV
Draw out the negative feedback loop of ADH regulation
Osmolarity of extracellular fluid increases-> signals osmoreceptors in hypothalamus-> activity of neurosecretory cells in hypothalamus increases-> signals posteriors pituitary-> ADH secretion increases-> signals kidneys-> water reabsorption increases-> water excretion decreases-> conservation of body water
Draw out the negative feedback loop that occurs when decreased blood pressure stimulates ADH release
MAP decreases-> signals arterial baroreceptors-> frequency of APs conducted to CNS decreases-> activity of neurosecretory cells in hypothalamus increases-> signals posteriors pituitary-> ADH secretion increases-> signals kidneys-> water reabsorption increases-> water excretion decreases-> conservation of BV
Draw out the negative feedback loop that occurs when BV decrease stimulates ADH release
BV decreases-> signals cardiac and venous baroreceptors-> frequency of APs conducted to CNS decreases-> activity of neurosecretory cells in hypothalamus increases-> signals posterior pituitary-> ADH secretion increases-> signals kidneys-> water reabsorption increases-> water excretion decreases-> conservation of BV
- decreased BV causes decreased MAP
What is another name for ADH?
- Vasopressin
- vasopressin receptor gene expressed in brain linked to monogamy + pair bonding in various species
- different variations of gene are linked to varying degrees of commitment to a mate
- environment + water access impacts monogamy bc limited resources means monogamy is Morse resourceful option to keep species going
- monogamy less necessary with ample water source
What is the renin-angiotensin mechanism?
- mediated but juxtaglomerular apparatus of the renal tubules
- when cells of JG apparatus are stimulated by low BP, enzyme renin is released into blood by granular cells of the kidney
- release of renin begins cascade of events that lead to release of angiotensin II
- net result is increase in BV + BP
What is angiotensin II?
Causes vasoconstriction to increase MAP, increase in thirst, increase in sympathetic activity, and leads to aldosterone and ADH release
- results in increased BV + BP
- original stimulus was low BP
How does aldosterone affect sodium reabsorption?
- increases sodium reabsorption, water follows sodium
What is aldosterone?
- steroid hormone (cholesterol is precursor for synthesis)
- increases osmolarity
- increases BV which increases BP
- secreted from adrenal cortex
- acts on principal cells of distal tubules and collecting ducts )increases number of Na+/K+ pumps on basolateral membrane; increases number of open Na+ and K+ channels on apical membrane
Draw out the mechanisms of aldosterone release and sodium reabsorption
1) BP falls-> 2) renin is released + signals angiotensinogen to release angiotensin I-> 3) angiotensin converting enzyme (ACE) signals release of angiotensin II-> 4) angiotensin II signals aldosterone release from adrenal cortex-> aldosterone causes salt retention which causes BP to rise
-> angiotensin II can also stimulate ADH release which causes BP to rise without aldosterone
-> angiotensin II can also cause vasoconstriction which increases BP
How does aldosterone impact K+ while increasing Na+ reabsorption?
Increases K+ secretion
What does Angiotensin II do?
- works to increase BP and BV
- stimulates aldosterone + ADH release
- is a vasoconstrictor + increases MAP
- stimulates sympathetic activity
- increases thirst
How does reabsorption regulation primarily occur?
By hormones
How does ADH regulate water and electrolyte reabsorption?
- prevents excessive water loss in urine
- causes kidney’s collecting ducts to reabsorb more water
- levels go up at night and is inhibited by alcohol
How is water and electrolyte reabsorption regulated by diabetes insipidus?
- occurs when ADH isn’t released
- leads to huge outputs of dilute urine without drinking a lot of water
- frequent bed wetting is a symptom
- rare
How is water and electrolyte reabsorption regulated by aldosterone?
- increased osmolarity
- regulates sodium ion content of ECF
- sodium is the electrolyte most responsible for osmotic water flow
- aldosterone promotes reabsorption of Na+ and water follows Na+
What is atrial natriuretic peptide?
- a peptide hormone
- released from atrium in response to stretch of wall
- increases sodium excretion
- antagonist of aldosterone and ADH (decreases BP + BV)
Draw out the negative feedback loop of ANP
Increased plasma volume-> increased atrial wall stretch-> increased ANP secretion-> afferent arteriole dilation + efferent arteriole contraction + renin secretion decreases-> glomerular capillary pressure increases + aldosterone decreases-> GFR increases + Na+ reabsorption decreases-> Na+ excretion increases
How does angiotensin II impact aldosterone and ADH?
Increases aldosterone + ADH secretion and thirst
How does ANP impact aldosterone and ADH secretion?
Decreases both
Is it more important to fix osmolarity issues or blood volume issues first?
osmolarity is more important bc it affects how the nervous system functions
What are the major acids and bases produced by the body?
- Phosphoric acid, lactic acid, fatty acids, CO2 forms carbonic acid
- ammonia/base
What are the three main lines of defense against acid-base disturbances?
- most balance maintained by kidneys (by maintaining H+ and bicarbonate)
- buffering of H+ ions (almost instant)
- respiratory compensation (takes minutes)
- renal compensation (hours to days)
What are the three major chemical buffer systems?
-bicarbonate buffer system: most important ECF buffer
- phosphate buffer system: incracellular
- protein buffer system
- hemoglobin (buffer in erythrocytes)
What are buffers?
Molecules that react to prevent dramatic changes in H+ conc.
- bind to H+ when pH drops
- release H+ when pH rises
What is the respiratory defense mechanism for acid-base balance?
- CO2 in the blood converted to bicarbonate ion + transported in the plasma
- CO2 increases amount of carbonic acid leading to more H+ ions
- excess acid can be blown off with release of CO2 from lungs
- respiratory rates rise/fall depending on changing blood pH
- hypoventilation decreases pH (more carbonic acid)
- hyperventilation increases pH (less carbonic acid)
What is respiratory compensation?
- 2nd line of defense
- take minutes to have effect
- regulates pH through varying ventilation
- increase ventilation-> decrease CO2-> decrease H+/increase pH
- decrease ventilation-> increases CO2-> increase H+/decrease pH
What is renal compensation?
-3rd line of defense
- regulate excretion of H+ and bicarbonate in urine
- urine pH varies from 4.5-8.0 depending on acid base balance
- regulate synthesis of new bicarbonate in renal tubules
How does renal compensation respond when blood pH falls and increases acidity?
1) increased secretion of hydrogen ions
2) increased reabsorption of bicarbonate
3) increased synthesis of new bicarbonate
How does renal compensation respond to increased pH and alkalinity?
1) decreased secretion of H+ ions
2) decreased reabsorption of bicarbonate
3) decreased synthesis of new bicarbonate
What are some respiratory disturbances to acid-base balance?
- CO2 is a source of acid + issues w/ controlling breathing rate may lead to changes in blood plasma pH
- Normal Pco2 arterial blood = 40mmHg
- Sources of CO2: cellular respiration
- Output of CO2: through respiratory system
- increase in plasma CO2-> respiratory acidosis
- decrease in plasma CO2-> respiratory alkalosis
What is respiratory acidosis?
-increased CO2-> increased H+-> decreased pH
- caused by hypoventilation due to a pathology
- compensation: renal
1) increase H+ secretion
2) increase bicarbonate reabsorption
3) increase synthesis of bicarbonate
- no effect on increased CO2
What is respiratory alkalosis?
Decreased CO2-> decreased H+-> increased pH
- caused by hyperventilation due to a pathology
- compensation: renal (effect on decreased CO2)
1) decrease H+ secretion
2) decrease bicarbonate reabsorption
3) decrease bicarbonate synthesis
What is metabolic acidosis?
- decrease pH through something other than carbon dioxide (usually low free bicarbonate)
- caused by high protein diet, height fat diet, heavy exercise, severe diarrhea, renal dysfunction/failure
- renal and respiratory compensation unless cause is renal
- respiratory compensation is increased ventilation-> decreased CO2
-renal compensation
1) increase H+ secretion
2) increase bicarbonate reabsorption
3) increase synthesis of new bicarbonate
What is metabolic alkalosis?
- Increase pH through something other than CO2 (usually high free bicarbonate)
- excessive vomiting
-consumption of alkaline products - renal dysfuntion/failure
- compensation is renal and respiratory
- respiratory compensation is decrease ventilation-> increase CO2 + neutralize alkalosis
- renal compensation
1) decrease H+ secretion
2) decrease HCO3- reabsorption
3) decrease synthesis of new bicarbonate
How should acid-base disturbances be evaluated?
See slide 81 for chart to memorize + practice
